Worse gas mileage after I added some fuel system cleaner

When I first got my jeep, if i let the gas light come on it would reach 300 miles. So I thought since its a 96 and noone has done it I would add some STP fuel system cleaner. So I added it at my last fill up. I am at a quarter of a tank left and I have only gone 185 miles. Its all city/highway same as when I could get the 300. Does the cleaner cause it to burn quicker or something like that, it is very suspicious.

No it shouldn't. There are three possibilities:

1. You didn't fill the tank up completely at the last fill-up, so you haven't really consumed 3/4 of a tank of gas in 185 miles.

2. Your fuel gauge may be acting up.

3. Your fuel consumption really has increased. I don't think the injector cleaner could have caused it. Probably the commonest cause of a sudden increase in fuel consumption is a bad O2 sensor.

Wait till the low fuel warning light comes on, see how many miles you did, and note much much fuel you needed to refill the tank to determine how many mpg you're getting.

Hmm.. Maybe I need to replace my O2 sensor.

I never bother to check MPGs "for record" after cleaning the TB and adding a can of Seafoam or Lucas to the tank... I'll wait till after that tankful has burned through.

Also be sure when you fill the tank for record, use the SAME pump and just let it quit when the auto shutoff tells it to. Checking MPGs while varying pumps and filling stations is not meaningless, but much less accurate than by reducing the variables.

Well I filled her up because the gas light on for 3 days was scaring me haha. I added 15.8 and I had gone 203 miles so I am getting 13.2mpg and mind you this is completely stock. Tomorrow I am going to autozone to get a new O2 sensor to see if its the fix.

xjrrrdx said:

Well I filled her up because the gas light on for 3 days was scaring me haha. I added 15.8 and I had gone 203 miles so I am getting 13.2mpg and mind you this is completely stock. Tomorrow I am going to autozone to get a new O2 sensor to see if its the fix.

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Wow when I see the gas light that means I need to fill up ASAP with 3 days of driving you're lucky

In any case wait one more tankfull before you go spend money on a sensor. Woody makes quite a few great points about filling up the gas tank and making your calculations more reliable. Also when you're filling up try to fill up at the same time of the day after same amount of driving at similar weather: if you wanna decrease even more variables you gotta take into account volume change with temp change. When I had some issues with the fuel economy on the XJ I had to play that game for a while till I got everything squared away (temp change seemed to have made more difference then I originally thought).

Calculating miles up to the point of when does the low fuel light come on is somewhat iffy as those floaters are not most reliable.

Once my refill light goes on, I over 70 miles left. On my previous XJ, I only had 30.

is there a fuel smell?
i just went thru something similar... i have been putting in a can of the B12 in every other tank for the past month... then all of a sudden my mileage went to crap.... and started to smell fuel... but no leak could be found... last week I filled up at the pump and the next day I was at a 1/3 of a tank. This time with the jeep running I watched under the rig... then I saw a drip.... the connection to my fuel rail was bad but only dripping when the engine was running and who knows how bad at highway speeds... the orings were toast... i changed them out and my mileage is back to about 19mpg.

Ditto on the fuel gauge inconsistency. Time before last I filled up when the tank read empty, (last mark) and put almost 22 gallons (yep 22) and this time around it only took 18.3 to fill from the same gauge reading. Oh, and I have been averaging around 13-14mpg in town, 01 Sport with AW4 and completely stock with fresh tuneup and K&N filter. If a new O2 sensor would help I would definetly change it but I think it is the nature of the beast. Check your tire psi, I run at 35 and it helps a little.

The cheaper FI cleaners are not such a bargain, they tend to dilute the fuel or cause other problems. They can also cause problems with seals. Generally the accepted cleaners are Chevron Techron, $9 a bottle, SeaFoam $6-7 a bottle, Valvoline gold, $8 a bottle. Some have reported good results with B12 but I've never tried it myself. When I do my annual cleaning I use the 3M system that attaches to the fuel rail and comes with a cleaner/fuel that runs about 20 min or so, puts a concentrated fuel/cleaner thru the injectors and engine, then over the year I dump a big bottle of Techron or Valvoline gold in there every couple of months. I'm always afraid of the cheap stuff, the possiblity exists that it can damage your O2 sensors or cat even though they say 'safe for 02 and cat's', kind of like the spray cleaners for the throttle body, according to all their labels they are 'safe' but 90% of them will eat the sensor plastic on the throttle body, I think their definition of 'safe' is you won't immeadiatly die if you use it . It is also possible that it broke some splooge loose in the system and you may have a partially clogged injector or two or 6.
I'd dump a large bottle of techron in there, comes in two sizes, full tank, see what happens. When I use it my milage does go down but not that drastically, maybe 2-3mpg but then it comes back after a couple of fillups. good luck...

Kejtar said:

Wow when I see the gas light that means I need to fill up ASAP with 3 days of driving you're lucky

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Heck, when I have the other vehicle parked for a while, I go thru an ENTIRE TANK in the XJ in three days!!

(Note: that's three 75-mile roundtrips... 225 miles. It wouldn't make it another 75, but would go quite a ways farther than 225!)

Den

try BG44K. Great stuff but expensive. Put one bottle (seemed small) in my tank last week and it runs better now than before.

you can try BGprod.com I think is the web site and find a shop near you that uses it. They will sell it to you. Costed me $28.00 with the gas drier bottle that came in the package.

i had echo clean or len somthin like that caost bout 11 bucks. seemd to run like crap xj had been sitting a while so i cleaned the system. thinkin bout doin it again but ill have to save for awile to afford a full tank of gas

i forgot to add i get very poor gas milage havnt done a check but seems like im at the gas station alot guess ill do a check soon.

I put some cleaner in a Ford Ranger I had one time...it immediately ran like crap soon afterward.

I noticed a black sooty smoke at the tailpipe (rich fuel mixture). It also smelled very strong from the tailpipe.

Turned out that the fuel pressure regulator was ruined internally. Replaced it and it was good to go after that.

I have never used that stuff since. I periodically use Chevron fuel that is blended with techroline.

RichP said:

The cheaper FI cleaners are not such a bargain, they tend to dilute the fuel or cause other problems. They can also cause problems with seals. Generally the accepted cleaners are Chevron Techron, $9 a bottle, SeaFoam $6-7 a bottle, Valvoline gold, $8 a bottle. Some have reported good results with B12 but I've never tried it myself.

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B12 seems to be good stuff. I've only had positive results, similar to SeaFoam.

I second the BG44K, I pay about $15 a can but well worth it. BTW its what all the dealerships around here use.

Well I filled up and I went driving around town and gas seems to be MUCH better. When I added the STP cleaner at 30 miles i already used 1/4 tank, now I am at 55 miles and I am still barely above 1/4 used. So there is some drastic improvement.